All these ones are long stories, people enter relationship for many reasons including sex, financial reason and maybe marriage, you want something from me, I want something from you and we start dating. That's how it works.

Marriage too is a business contract.

In as much the OP made some salient points, the truth still remains that there are no sure guide in relationships. What works for others might not work someone. Seen those who dated for many years and ended with so much marriage crisis to the point that I asked myself, all those years of dating, what was been done. Had an u clear who met a girl dated her for two months and they are fine till date since six years...

Some are just been lucky in relationships while others are not buh most times due to infatuation and so called blinded lust do not see or choose to ignore red flags...